U.S. patent application number 11/867464 was filed with the patent office on 2008-05-22 for photoelectric conversion element, method of manufacturing the same and solar cell.
This patent application is currently assigned to KONICA MINOLTA BUSINESS TECHNOLOGIES, INC.. Invention is credited to Akihiko ITAMI, Fumitaka MOCHIZUKI, Kazukuni NISHIMURA.
Application Number | 20080115826 11/867464 |
Document ID | / |
Family ID | 39415724 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080115826 |
Kind Code |
A1 |
NISHIMURA; Kazukuni ; et
al. |
May 22, 2008 |
PHOTOELECTRIC CONVERSION ELEMENT, METHOD OF MANUFACTURING THE SAME
AND SOLAR CELL
Abstract
A photoelectric conversion element comprising an electrically
conductive support having thereon an oxide semiconductor electrode
comprising an oxide semiconductor which is adsorbed with a dye, and
a counter electrode facing the oxide semiconductor electrode
through a charge transfer layer, wherein the dye is represented by
Formula (1): ##STR00001##
Inventors: |
NISHIMURA; Kazukuni; (Tokyo,
JP) ; ITAMI; Akihiko; (Tokyo, JP) ; MOCHIZUKI;
Fumitaka; (Tokyo, JP) |
Correspondence
Address: |
LUCAS & MERCANTI, LLP
475 PARK AVENUE SOUTH, 15TH FLOOR
NEW YORK
NY
10016
US
|
Assignee: |
KONICA MINOLTA BUSINESS
TECHNOLOGIES, INC.
Tokyo
JP
|
Family ID: |
39415724 |
Appl. No.: |
11/867464 |
Filed: |
October 4, 2007 |
Current U.S.
Class: |
136/252 ;
257/E31.026; 438/95 |
Current CPC
Class: |
Y02E 10/549 20130101;
Y02P 70/521 20151101; H01G 9/2059 20130101; H01L 51/006 20130101;
H01L 51/0053 20130101; Y02E 10/542 20130101; H01L 51/0065 20130101;
H01L 51/4226 20130101; H01L 2251/306 20130101; H01G 9/2031
20130101; H01L 51/0059 20130101; Y02P 70/50 20151101; H01L 51/0068
20130101; H01L 51/0061 20130101 |
Class at
Publication: |
136/252 ; 438/95;
257/E31.026 |
International
Class: |
H01L 31/04 20060101
H01L031/04; H01L 31/18 20060101 H01L031/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 20, 2006 |
JP |
2006312615 |
Claims
1. A photoelectric conversion element comprising an electrically
conductive support having thereon an oxide semiconductor electrode
comprising an oxide semiconductor which is adsorbed with a dye, and
a counter electrode facing the oxide semiconductor electrode
through a charge transfer layer, wherein the dye is represented by
Formula (1): ##STR00013## wherein R.sub.1 represents an alkyl
group, an aralkyl group, an alkenyl group, an aryl group or an
aromatic heterocyclic group; R.sub.2 represents a divalent group
containing an aromatic hydrocarbon ring, a divalent group
containing an aromatic heterocycle or a divalent group containing
an aromatic hydrocarbon ring and an aromatic heterocycle; R.sub.3
represents a hydrogen atom, an alkyl group, an aralkyl group, an
alkenyl group, an aryl group or an aromatic heterocyclic group;
R.sub.4 represents an aryl group; R.sub.5 represents a substituent;
n1 is 0 or 1; n2 and n3 each are 1 or 2; n1+n2+n3=3; n4 is an
integer of not less than 0; n5 is an integer of 0-4; and A
represents a chain structure containing an electron withdrawing
group and an acid group, provided that R.sub.2 is .pi.-conjugated
with the acid group, or A represents a group represented by
A.sub.2, ##STR00014## wherein B represents a group of atoms
necessary to form a single ring which may have a substituent,
provided that the single ring is not condensed with another ring
nor substituted with another ring; and X represents a group
containing an acid group.
2. The photoelectric conversion element of claim 1, wherein n1 in
Formula (1) is 0, and R.sub.2 is a phenylene group.
3. The photoelectric conversion element of claim 1, wherein n4 in
Formula (1) is 0.
4. The photoelectric conversion element of claim 1, wherein A in
Formula (1) represents a cyanoacrylic acid group.
5. The photoelectric conversion element of claim 1, wherein A in
Formula (1) is represented by A.sub.2 and A.sub.2 represents a
rhodanine-N-acetic acid group.
6. The photoelectric conversion element of claim 1, wherein the dye
is Dye (1): ##STR00015##
7. The photoelectric conversion element of claim 1, wherein the dye
is Dye (2): ##STR00016##
8. The photoelectric conversion element of claim 1, wherein the dye
is Dye (3): ##STR00017##
9. The photoelectric conversion element of claim 1, wherein the dye
is Dye (4): ##STR00018##
10. The photoelectric conversion element of claim 1, wherein the
dye is Dye (5): ##STR00019##
11. The photoelectric conversion element of claim 1, wherein the
dye is Dye (6): ##STR00020##
12. The photoelectric conversion element of claim 1, wherein the
dye is Dye (7): ##STR00021##
13. The photoelectric conversion element of claim 1, wherein the
dye is Dye (8): ##STR00022##
14. The photoelectric conversion element of claim 1, wherein the
oxide semiconductor includes titanium oxide.
15. The photoelectric conversion element of claim 1, wherein a
thickness of the oxide semiconductor electrode is 100 to 10000
nm.
16. The photoelectric conversion element of claim 1, wherein a
3-methylpropionitrile solution containing lithium iodide, iodine
and 4-(t-butyl)pyridine is used in the charge transfer layer.
17. A solar cell comprising the photoelectric conversion element of
claim 1.
18. A method of manufacturing the photoelectric conversion element
of claim 1 comprising: applying oxide semiconductor particles on
the electrically conductive support; calcinating the applied oxide
semiconductor particles; adsorbing the dye on the calcinated oxide
semiconductor particles to form the oxide semiconductor electrode;
providing the charge transfer layer on the oxide semiconductor
electrode; and providing the counter electrode on the charge
transfer layer.
19. The method of claim 18, wherein the dye is adsorbed on the
calcinated oxide semiconductor particles before water is adsorbed
on the calcinated oxide semiconductor particles.
20. The method of claim 18, wherein the calcinated oxide
semiconductor particles is soaked in a solution containing the dye
for 3 to 48 hours at 25.degree. C. to adsorb the dye.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a dye sensitized
photoelectric conversion element, a method of manufacturing the
same and a solar cell utilizing the photoelectric conversion
element.
BACKGROUND OF THE INVENTION
[0002] In recent years, extensive studies have been made to utilize
the sunlight which is limited and generates no toxic substances.
Examples of the practical application of sunlight which is a clean
energy source, at present, include inorganic solar cells for a
residential application such as single crystalline silicon,
polycrystalline silicon, amorphous silicon, cadmium telluride and
indium-copper selenide.
[0003] However, one of the disadvantages of these inorganic solar
cells is that, for example, in the case of a silicon solar cell,
very high purity silicon is required, in which, naturally, the
purification process is complicated and numerous processes are
included, resulting in a high manufacturing cost.
[0004] On the other hand, many solar cells utilizing an organic
material have also been proposed. Examples of an organic solar cell
include: (i) a Schottky-type photoelectric conversion element in
which a p-type organic semiconductor and a metal having a small
work function are connected; and (ii) a hetero-connection type
photoelectric conversion element, in which a p-type organic
semiconductor and an n-type inorganic semiconductor are connected
or a p-type organic semiconductor and an electron accepting organic
compound are connected. Organic semiconductors utilized in such an
organic solar cell include, for example, a synthetic dye or a
pigment such as chlorophyll and perylene; and a conductive polymer
material such as polyacetylene, and complex materials thereof.
These materials are made into thin film, by such as a vacuum
evaporation method, a casting method or a dipping method, which
constitutes a battery material. The organic material has
advantages, for example, a low cost and easy application to a
larger area; however, there are also problems, for example,
conversion efficiency as low as not more than 1% in many materials;
and poor durability.
[0005] In such a situation, a solar cell exhibiting excellent
characteristics has been reported by Dr. Gratzel et al.,
Switzerland (for example, refer to Non-Patent Document 1). The
proposed cell is a dye sensitized solar cell, and is a wet type
solar cell utilizing titanium oxide porous thin film, which is
spectrally sensitized by a ruthenium complex, as a working
electrode. Advantages of this method are that (i) a low priced
oxide semiconductor such as titanium oxide can be used and the
purification up to a high purity of this material is not required,
resulting in attaining a low cost; and that (ii) usable light
covers a broad visible light region, which enables efficient
conversion of sunlight to electricity, since sunlight is rich in a
visible light component.
[0006] On the contrary, since a ruthenium complex having a resource
limitation is utilized, supply of a ruthenium complex is uncertain
when this solar cell is utilized in practice. Further, this
ruthenium complex is expensive and has a problem of stability in
aging, however, this problem will be overcome if the material can
be changed into a low priced and stable organic dye.
[0007] It has been disclosed that an element having high
photoelectric conversion efficiency can be obtained when a compound
having a triphenylamine structure is utilized (for example, refer
to Patent Document 1). However, these dyes have a problem of
durability, which is remained as a problem to be solved.
[0008] Patent Document 1 Japanese Patent Application Publication
Open to Public Inspection No. 2005-123033 (hereinafter, referred to
as JP-A No.)
[0009] Non-Patent Document 1 B. O' Regan, M. Gratzel, Nature, 353,
737
SUMMARY OF THE INVENTION
[0010] An object of the present invention is to provide a dye
sensitized photoelectric conversion element exhibiting high
photoelectric conversion efficiency and high durability, a method
of manufacturing the same and a solar cell using said photoelectric
conversion element.
[0011] One of the aspects to achieve the above object of the
present invention is a photoelectric conversion element comprising
an electrically conductive support having thereon an oxide
semiconductor electrode comprising an oxide semiconductor which is
adsorbed with a dye, and a counter electrode facing the oxide
semiconductor electrode through a charge transfer layer, wherein
the dye is represented by Formula (1):
##STR00002##
wherein R.sub.1 represents an alkyl group, an aralkyl group, an
alkenyl group, an aryl group or an aromatic heterocyclic group;
R.sub.2 represents a divalent group containing an aromatic
hydrocarbon ring, a divalent group containing an aromatic
heterocycle or a divalent group containing an aromatic hydrocarbon
ring and an aromatic heterocycle; R.sub.3 represents a hydrogen
atom, an alkyl group, an aralkyl group, an alkenyl group, an aryl
group or an aromatic heterocyclic group; R.sub.4 represents an aryl
group; R.sub.5 represents a substituent; n1 is 0 or 1; n2 and n3
each are 1 or 2; n1+n2+n3=3; n4 is an integer of not less than 0;
n5 is an integer of 0-4; and A represents a chain structure
containing an electron withdrawing group and an acid group,
provided that R.sub.2 is .pi.-conjugated with the acid group, or A
represents a group represented by A.sub.2,
##STR00003##
wherein B represents a group of atoms necessary to form a single
ring which may have a substituent, provided that the single ring is
not condensed with another ring nor substituted with another ring;
and X represents a group containing an acid group.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] According to the present invention, a dye sensitized
photoelectric conversion element having high photoelectric
conversion efficiency and high durability, and a solar cell using
said photoelectric conversion element can be provided.
[0013] In the following, the present invention will be
detailed.
[0014] Since the sensitizing dye generates current by repeating a
photo-oxidation reaction at the time of power generation, it has
been assumed in the present invention that a dye having a strong
resistance to oxidation is suitable for improving the durability of
the photoelectric conversion element. Therefore, among the
compounds provided with a triphenylamine structure, selected has
been a structure, in which styryltriphenylamine exhibiting high
durability against ozone which is a strong oxidizing agent is
employed as a central moiety of a sensitizing dye and a chelate
bonding with titanium oxide is made possible by addition of an acid
group which enables efficient transfer of an photo-excited electron
to titanium oxide. Further, to increase transfer efficiency of a
photo-excited electron, a styryltriphenylamine central moiety and
an acid group are connected by an electron withdrawing .pi.
conjugated system. Thus, a new sensitizing dye exhibiting a high
photoelectric conversion efficiency and high durability has been
found, when used in a dye sensitized photoelectric conversion
element.
[0015] <Oxide Semiconductor>
[0016] Examples of an oxide semiconductor utilized for the oxide
semiconductor electrode of the present invention include: elemental
substances such as silicon and germanium; compounds containing an
element of Groups 3-5 and Groups 13-15 of the periodic table (also
referred to as the element periodic table); sulfides, selenides and
nitrides of the abovementioned metals.
[0017] Examples of a preferable metal oxide include: oxides of
titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium,
indium, cerium, yttrium, lanthanum, vanadium, niobium or tantalum.
Examples of a compound which can be incorporated in the oxide
electrode include: sulfides of cadmium, zinc, silver, antimony and
bismuth; selenides of cadmium and lead; a telluride of cadmium;
phosphides of zinc, gallium, indium and cadmium; selenides of
gallium-arsenic and copper-indium; and a sulfide of copper-indium
and a nitride of titanium.
[0018] Specific examples of the abovementioned compound include:
TiO.sub.2, SnO.sub.2, Fe.sub.2O.sub.3, WO.sub.3, ZnO,
Nb.sub.2O.sub.5, CdS, ZnS, PbS, Bi.sub.2S.sub.3, CdSe, CdTe, GaP,
InP, GaAs, CuInS.sub.2, CuInSe.sub.2 and Ti.sub.3N.sub.4. Of these,
preferably utilized are TiO.sub.2, ZnO, SnO.sub.2, Fe.sub.2O.sub.3,
WO.sub.3, Nb.sub.2O.sub.5, CdS and PbS; more preferably utilized
are TiO.sub.2 and Nb.sub.2O.sub.5; and most preferably utilized is
TiO.sub.2.
[0019] In the oxide semiconductor electrode of the present
invention, the above-described plural semiconductors may be
utilized in combination. For example, a few types of the above
described metal oxides or metal sulfides may be utilized in
combination, or utilized may be a titanium oxide semiconductor
mixed with 20 weight % of titanium nitride (Ti.sub.3N.sub.4).
Further, zinc oxide/tin oxide complex, described in J. Chem. Soc.,
Chem. Commun., 15 (1999), may also be utilized. In the case when a
component other than a metal oxide and a metal sulfide is added in
the semiconductor, the weight ratio of the additional component to
a metal oxide or a metal sulfide semiconductor is preferably not
more than 30%.
[0020] <Sensitization Treatment>
[0021] The above-described oxide semiconductor is subjected to a
sensitization treatment by a dye represented by aforesaid Formula
(1) to prepare a photoelectric conversion element of the present
invention exhibiting excellent photoelectric conversion efficiency
and durability, which is an object of the present invention.
[0022] In the following, the dye represented by aforesaid Formula
(1) of the present invention (hereinafter, also simply referred to
as dye) will be explained.
[0023] In Formula (1), R.sub.1 is an alkyl group, an aralkyl group,
an alkenyl group, an aryl group or an aromatic heterocyclic group;
R.sub.2 is a divalent group containing an aromatic hydrocarbon
ring, a divalent group containing an aromatic heterocycle or a
divalent group containing an aromatic hydrocarbon ring and an
aromatic heterocycle; R.sub.3 is a hydrogen atom, an alkyl group,
an aralkyl group, an alkenyl group, an aryl group or an aromatic
heterocyclic group; R.sub.4 is an aryl group; and R.sub.5 is a
substituent. n1 is 0 or 1; n2 and n3 each are 1 or 2; and
n1+n2+n3=3. n4 is an integer of not less than 0, and n5 is an
integer of 0-4. Herein, the upper limit of n4 is 10.
[0024] Examples of a substituent represented by R.sub.5 include: an
alkyl group, an aralkyl group, an alkoxy group, a halogen atom, an
alkenyl group, an aryl group and an aromatic heterocyclic group.
Each of an aryl group and an aromatic heterocyclic group
represented by R.sub.1 and R.sub.3; an aromatic hydrocarbon ring, a
heterocycle and an aromatic hydrocarbon ring-aromatic heterocycle
in R.sub.2; and an aryl group represented by R.sub.4 may have a
substituent, and as the substituent, the above mentioned
substituents described for R.sub.5 can be cited.
[0025] In Formula (1), A represents a chain structure containing an
electron withdrawing group and an acid group, in which R.sub.2 is
.pi.-conjugated with the acid group, or A represents a group
represented by A.sub.2 shown above. In A.sub.2, B is a group of
atoms necessary to form a single ring which may have a substituent.
The substituent includes, for example, a halogen atom, a cyano
group, a carbonyl group, a thiocarbonyl group, a selenocarbonyl
group and an alkyl group. However, said monocyclic ring is not
condensed with another rings or is not substituted with another
rings. X is a group having an acid group.
[0026] Specific examples of an acid group include a carboxylic acid
group (--COOH), phosphorous acid group (--PO(OH).sub.2) and
sulfonic acid group (--SO.sub.2OH). The acid group portion may also
be a metal salt or an organic cationic salt. Further, a group
having an acid group represented by X specifically includes
-alkylene-COOH, -arylene-COOH, -alkylene-PO(OH).sub.2 and
.dbd.C(CN)COOH.
[0027] An electron withdrawing group is preferably a substituent
having a Hammett's substitution constant up value of not less than
0.01, and more preferably of not less than 0.1. With respect to a
Hammett's substitution constant, such as Journal of Medicinal
Chemistry, 1973, Vol. 16, No. 11, pp. 1207-1216 can be referred
to.
[0028] An electron withdrawing group includes, for example, a
halogen atom (fluorine atom (.sigma.p value: 0.06), chlorine atom
(.sigma.p value: 0.23), bromine atom (.sigma.p value: 0.23), iodine
atom (.sigma.p value: 0.18)), a trihalomethyl group (tribromomethyl
(.sigma.p value: 0.29), trichloromethyl (.sigma.p value: 0.33),
trifluoromethyl (.sigma.p value: 0.54)), a cyano group (.sigma.p
value: 0.66), a nitro group (.sigma.p value: 0.78), aliphatic-aryl
or heterocyclic sulfonyl group (such as methanesulfonyl group
(.sigma.p value: 0.72)), aliphatic-aryl or heterocyclic acyl group
(such as acetyl (.sigma.p value: 0.50) and benzoyl (.sigma.p value:
0.43)), aliphatic-aryl or heterocyclic oxycarbonyl group (such as
methoxycarbonyl (.sigma.p value: 0.45) and phenoxycarbonyl
(.sigma.p value: 0.45)), a carbamoyl group (.sigma.p value: 0.36)
and a sulfamoyl group (.sigma.p value: 0.57).
[0029] Specific examples of R.sub.1 and R.sub.3 are shown
below.
##STR00004##
[0030] Specific examples of R.sub.2 are shown below.
##STR00005##
[0031] Specific examples of R.sub.4 are shown below.
##STR00006##
[0032] Specific examples of R.sub.5 are shown below.
##STR00007##
[0033] Specific examples of a chain structure containing an
electron withdrawing group and an acid group and forms a .pi.
conjugation system between R.sub.2 and the acid group, will be
shown in the following.
##STR00008##
[0034] Further, specific examples of A.sub.2 will be shown
below.
##STR00009##
[0035] In the following, specific examples of a dye represented by
Formula (1) of the present invention will be shown, however, the
present invention is not limited thereto.
##STR00010## ##STR00011##
[0036] In the following, a specific synthesis method of the dye
represented by Formula (1) of the present invention will be shown,
however, other dye can be synthesized in a similar manner and the
synthesis method is not limited thereto.
[0037] Synthesis of Dye (1) 4-(2,2-diphenylvinyl)-triphenylamine
was added with 6 equivalents of phosphorus oxychloride and 8
equivalents of N,N'-dimethylformamide, and diformylation was
carried out by heating at 90.degree. C. for 16 hours under a
nitrogen atmosphere. An acetic acid solution containing a diformyl
substance, 2 equivalents of cyanoacetic acid and 2.2 equivalents of
ammonium acetate was refluxed with heating for 1 hour, whereby dye
(1) has been prepared.
[0038] Synthesis of Dye (2)
[0039] Dye (2) has been synthesized in a similar manner to
synthesis of dye (1) except that rhodanin-N-acetic acid was
utilized instead of cyanoacetic acid.
[0040] An oxide semiconductor of the present invention is
sensitized by incorporating a dye represented by aforesaid Formula
(1) and enables to exhibit the effects described in the present
invention. Incorporate said dye in the oxide electrode includes
various embodiments such as adsorption on the semiconductor
surface, and getting the aforesaid dye into a porous structure when
a semiconductor is provided with a porous structure.
[0041] Further, the total content of each dye represented by
aforesaid Formula (1) per 1 m.sup.2 of a semiconductor is
preferably in a range of 0.01-100 mmol, more preferably 0.1-50 mmol
and specifically preferably 0.5-20 mmol.
[0042] In the case of performing a sensitization treatment by use
of the dye represented by aforesaid Formula (1) of the present
invention, the aforesaid dye may be utilized alone; or a plurality
of dyes may be utilized in combination. Further, a dye represented
by aforesaid Formula (1) of the present invention and other dye
(for example, dye described in such as U.S. Pat. Nos. 4,684,537,
4,927,721, 5,084,365, 5,350,644, 5,463,057 and 5,525,440; and JP-A
Nos. 7-249790 and 2000-150007) may be utilized in combination.
[0043] In particular, in the case that application of the
photoelectric conversion element of the present invention is a
solar cell, which will be described below, it is preferable to
utilize at least two kinds of dyes in combination so as to make a
wavelength region of photoelectric conversion as broad as possible
to effectively utilize sunlight.
[0044] To incorporate a dye represented by Formula (1) in an oxide
semiconductor, an ordinary method is to dissolve the aforesaid dye
in a suitable solvent (such as ethanol) and to immerse a
semiconductor having been well dried in said solution for a long
time.
[0045] In the case of performing a sensitization treatment
utilizing a plurality of dyes represented by aforesaid Formula (1)
together or said dye with another sensitizing dye in combination,
it can be performed by preparing a mixed solution of each dye, or
by preparing a solution of each dye and successively immersing
semiconductor in each solution. In the case of manufacturing by
preparation of a separate solution of each dye and successive
immersion in each solution, the effects of the present invention
can be obtained despite of the order of incorporation of such as
the aforesaid dye or other sensitizing dye in an oxide
semiconductor. Further, it is also possible, for example, to mix
plural kinds of semiconductor particles, each kind containing only
one of the above described dyes to prepare the oxide semiconductor
electrode.
[0046] The adsorption treatment may be performed when an oxide
semiconductor is in a particle state or after the particles have
been formed in to a film. The solution of the dye employed for the
adsorption treatment may be utilized at an ambient temperature or
may be utilized by heating within the temperature range where the
dye does not decompose nor the solution does not boil. Further, as
the later mentioned manufacturing process of a photoelectric
conversion element, adsorption of the dye may be carried out after
the application of semiconductor particles. Further, adsorption of
the dye may be carried out by simultaneously applying the
semiconductor particles and the dye of the present invention. The
dye not adsorbed by the semiconductor can be removed by
washing.
[0047] As for a sensitization treatment of the oxide semiconductor
of the present invention, a sensitization treatment is carried out
by incorporation of a dye represented by aforesaid Formula (1),
however, details of a sensitization treatment will be specifically
explained in an explanation of a photoelectric conversion element
which will be described later.
[0048] In the case of an oxide semiconductor having a semiconductor
thin film having a high porosity, it is preferable to complete an
adsorption treatment of such as the aforesaid dye or other
sensitizing dye (a sensitization treatment of an oxide
semiconductor) before the water or water vapor adsorbs on
semiconductor film and voids of the interior of semiconductor thin
film.
[0049] An oxide semiconductor of the present invention may be
subjected to a surface treatment by use of an organic base. The
aforesaid organic base includes, for example, diarylamine,
triarylamine, pyridine, 4-t-butylpyridine, polyvinyl pyridine,
quinoline, piperidine and amidine, however, preferable among them
are pyridine, 4-t-butylpyridine and polyvinyl pyridine.
[0050] The surface treatment can be carried out by using the
aforesaid organic base as it is when it is a liquid, or by
preparing a solution of an organic base dissolved in an organic
solvent when it is a solid, and by immersing an oxide semiconductor
of the present invention in liquid amine or in an amine
solution.
[0051] As the dye usable together with the dye represented by
aforesaid Formula (1), any dye can be utilized as far as being
capable of spectral sensitization of the oxide semiconductor of the
present invention. It is preferable to mix at least two different
dyes to make a wavelength region of photoelectric conversion as
broad as possible and to increase conversion efficiency. Further,
the types of dyes to be mixed and the mixing ratio thereof can be
selected to match the wavelength range and the strength
distribution of aimed light source.
[0052] Among the dyes utilized together, preferably employed are a
metal complex dye, a phthalocyanine dye, a porphyrin dye and a
polymethine dye from a comprehensive viewpoints of the activity for
a photoelectron transfer reaction, durability against light and
photochemical stability
[0053] [Photoelectric Conversion Element]
[0054] The photoelectric conversion element of the present
invention is constituted by arranging an oxide semiconductor
electrode, which is comprised of an electrically conductive support
having thereon an oxide semiconductor adsorbed with a dye, and a
counter electrode facing the oxide semiconductor electrode through
a charge transfer layer. In the following, an oxide semiconductor
electrode, a charge transfer layer and a counter electrode will be
explained.
[0055] <Oxide Semiconductor Electrode>
[0056] A preparation method of an oxide semiconductor electrode of
the present invention will now be explained.
[0057] An embodiment of an oxide semiconductor electrode of the
present invention includes a method to form the above-described
oxide semiconductor on a conductive support by calcination.
[0058] In the case of preparing an oxide semiconductor of the
present invention by calcination, a sensitizing treatment of said
semiconductor utilizing the above-described dye and other
sensitizing dye (such as adsorption and getting into a porous
substance) is preferably performed after calcination. After
calcination, it is preferable to quickly perform an adsorption
treatment of dye before water adsorbs on a semiconductor.
[0059] In the case of the oxide semiconductor of the present
invention being particles, an oxide semiconductor electrode is
preferably prepared by coating or spraying an oxide semiconductor
on a conductive support. Further, when the oxide semiconductor of
the present invention is a film which is not held on a conductive
support, the oxide semiconductor electrode film is preferably
pasted on a conductive support to prepare an oxide semiconductor
electrode.
[0060] (Electrically Conductive Support)
[0061] As an electrically conductive support (also referred to as
merely a conductive support) utilized for the photoelectric
conversion element of the present invention and the solar cell of
the present invention, utilized are those having a structure
comprising a conductive substance arranged on a non-conductive
material such as a glass plate or a plastic film. Examples of a
material utilized for a conductive support include a metal (such as
platinum, gold, silver, copper, aluminum, rhodium and indium), a
conductive metal oxide (such as an indium-tin complexing oxide and
tin oxide doped with fluorine) or carbon. Thickness of a conductive
support is not specifically limited, however, is preferably 0.3-5
mm.
[0062] The conductive support is preferably substantially
transparent. To be essentially transparent means to have a
transmittance of not less than 10%, more preferably of not less
than 50% and most preferably of not less than 80%. To obtain a
transparent support, it is preferable to provide a conductive layer
comprising a conductive metal oxide on the surface of a glass plate
or a plastic film. In the case of utilizing a transparent
conductive support, light is preferably incident from the support
side.
[0063] Surface resistance of a conductive support is preferably not
more than 5 .OMEGA./sq and more preferably not more than 10
.OMEGA./sq.
[0064] (Preparation of Coating Liquid Containing Oxide
Semiconductor Particles)
[0065] First a coating liquid containing fine powder of an oxide
semiconductor is prepared. The primary particle diameter of this
semiconductor fine powder is preferably smaller; the primary
particle diameter is preferably 1-5,000 nm and more preferably 2-50
nm. A coating liquid containing semiconductor fine powder can be
prepared by dispersing semiconductor fine powder in a solvent.
Semiconductor fine powder dispersed in a solvent is dispersed in a
state of the primary particle. Any solvent is usable as far as it
can disperse the fine powder and the solvent is not specifically
limited.
[0066] The aforesaid solvent includes, for example, water, an
organic solvent and a mixed solution of water and an organic
solvent. As an organic solvent, an alcohol such as methanol or
ethanol; a ketone such as methyl ethyl ketone, acetone or acetyl
acetone; and a hydrocarbon such as hexane or cyclohexane are
usable. In a coating liquid, a surfactant or a viscosity
controlling agent (such as a polyalcohol such as polyethylene
glycol) can be appropriately incorporated. A range of concentration
of a semiconductor fine powder in a solvent is preferably 0.1-70%
by weight and more preferably 0.1-30% by weight.
[0067] (Application of Coating Liquid Containing Semiconductor Fine
Powder and Calcination Treatment of Formed Semiconductor Layer)
[0068] A coating liquid containing semiconductor fine powder
prepared in the above manner is coated or sprayed on a conductive
support, followed by being dried, and is calcinated in air or in an
inert gas, whereby a semiconductor layer (semiconductor film) is
formed on a conductive support.
[0069] The film prepared by coating and drying the coating liquid
on a conductive support is comprised of aggregate of semiconductor
particles, and the particle diameter of the particles corresponds
to the primary particle diameter of utilized semiconductor fine
powder.
[0070] Since semiconductor particle aggregate film formed on a
substrate of such as a conductive support in this manner is weak in
bonding strength with a conductive support or in bonding strength
among particles each other as well as in mechanical strength, the
calcination treatment of the aforesaid semiconductor particle
aggregate film is preferably performed to increase mechanical
strength and to make calcinated film firmly adhered on a
substrate.
[0071] In the present invention, the calcinated film may have any
structure, however, preferable is a film having a porous structure
(having voids, also referred to as a porous layer).
[0072] The porosity of the semiconductor film of the present
invention is preferably not more than 10% by volume, more
preferably not more than 8% by volume and specifically preferably
0.01-5% by volume. A porosity of a semiconductor film means a
porosity penetrating in the thickness direction of a dielectric
substance, and can be measured by use of an apparatus available on
the market such as a mercury porosimeter (Shimazu Porelyzer
9220).
[0073] The layer thickness of the semiconductor layer containing a
calcinated substance film having a porous structure is preferably
at least not less than 10 nm and more preferably 100-10,000 nm.
[0074] At the time of a calcination treatment, the calcination
temperature is preferably not higher than 1,000.degree. C., more
preferably 200-800.degree. C. and specifically preferably
300-800.degree. C., in order to suitably control the actual surface
area of the calcinated film and to prepare the calcinated film
having the above-described porosity.
[0075] The ratio of an actual surface area to an apparent surface
area can be controlled by, for example, the particle diameter of
semiconductor particles and the calcination temperature. After the
calcination treatment, for the purpose of increasing a surface
area, and increasing the purity of titanium oxide in the vicinity
of semiconductor particles in order to increase electron injection
efficiency from dye to semiconductor particles, a chemical plating
treatment may be performed utilizing a titanium tetrachloride
aqueous solution or an electrochemical plating treatment may be
performed utilizing a titanium trichloride aqueous solution.
[0076] (Sensitization Treatment of Oxide Semiconductor)
[0077] A sensitization treatment of the oxide semiconductor is
performed by dissolving dye in a suitable solvent and immersing a
substrate, comprising the aforesaid semiconductor having been
calcinated, in the solution. At this time, the substrate formed by
calcinating a semiconductor layer (also referred to as
semiconductor film) is preferably subjected to a evacuation
treatment or a heating treatment to eliminate air bubbles in the
film so that the dye represented by aforesaid Formula (1) can
deeply enter into the interior of a semiconductor layer
(semiconductor film). Accordingly, it is specifically preferable
when the semiconductor layer (semiconductor film) is a porous
film.
[0078] A solvent utilized to dissolve dye represented by aforesaid
Formula (1) is not specifically limited as far as it dissolves said
dye and does not dissolve nor react with the semiconductor.
However, it is preferable that the solvent is degassed and purified
by distillation in advance to prevent moisture and air dissolved in
the solvent from entering into semiconductor film resulting in
prevention of a sensitization treatment such as by adsorption of
the aforesaid dye.
[0079] For dissolution of the aforesaid dye, examples of a
preferably utilized solvent include: alcohol solvents such as
methanol, ethanol and n-propanol; ketone solvents such as acetone
and methylethyl ketone; ether solvents such as diethyl ether,
diisopropyl ether, tetrahydrofuran and 1,4-dioxane; and a
hydrocarbon halogenide solvent such as methylene chloride and
1,1,2-trichloroethane. Of these, specifically preferable are
methanol, ethanol, acetone, methylethyl ketone, tetrahydrofuran and
methylene chloride.
[0080] (Temperature and Duration of Sensitization Treatment)
[0081] In order to sufficiently promote the adsorption of the
aforesaid dye by deeply penetrating into a semiconductor layer
(semiconductor film) to sufficiently sensitize the semiconductor,
and also to avoid the disturbance of the adsorption of the dye due
to the decomposition product of the dye in the solution, the
duration to immerse a substrate containing a calcinated oxide
semiconductor in a solution containing a dye represented by
aforesaid Formula (1) is preferably 3-48 hours and more preferably
4-24 hours, under a condition of 25.degree. C. This effect is
particularly significant when a semiconductor film is a porous
film. The above duration of immersion is a value under a condition
of 25.degree. C. and it is not the case when the temperature
condition is varied.
[0082] In the case of immersion, a solution containing the dye
represented by aforesaid Formula (1) may be used by heating the
solution within a temperature range where it does not boil,
provided that the dye does not decomposes. A preferable temperature
range is 10-100.degree. C. and more preferably 25-80.degree. C.;
however, it is not the case when a solvent boils in the aforesaid
temperature range, as described above.
[0083] <Charge Transfer Layer>
[0084] The charge transfer layer utilized in the present invention
will now be explained.
[0085] In a charge transfer layer a redox electrolyte is preferably
utilized. A redox electrolyte includes, for example, a
I.sup.-/I.sub.3.sup.- type, a Br.sup.-/Br.sub.3.sup.- type and a
quinone/hydroquinone type. These redox electrolytes can be prepared
by a method conventionally well known in the art, and for example,
an electrolyte of I.sup.-/I.sub.3.sup.- type can be prepared by
mixing iodine and an ammonium salt of iodine. A charge transfer
layer is constituted of a dispersion of these redox electrolytes.
The dispersion is referred to as (i) a liquid electrolyte when it
is a liquid, (ii) a solid polymer electrolyte when an electrolyte
is dispersed in polymer which is solid at ordinary temperature, and
(iii) a gel electrolyte when an electrolyte is dispersed in a gel
form substance. In the case that a liquid electrolyte is utilized
as a charge transfer layer, an electrochemically inert solvent is
used, of which examples include: acetonitrile, propylene carbonate
and ethylene carbonate. Examples of a solid electrolyte are
disclosed in JP-A 2001-160427, and examples of a gel electrolyte
are shown in "Surface Science", vol. 21, No. 5, pp. 288-293.
[0086] <Counter Electrode>
[0087] The counter electrode utilized in the present invention will
now be explained.
[0088] As a counter electrode, those having conductivity are
applicable and any conductive material is usable, however,
preferable is a material having a catalytic function to promote the
oxidation reaction of such as I.sub.3-- ions and the reduction
reaction of other redox ions to carry out at a sufficient rate.
Examples of such a material include: a platinum electrode, a
conductive material having a plated or evaporated platinum layer on
the surface, rhodium metal, ruthenium metal, ruthenium oxide and
carbon.
[0089] [Solar Cell]
[0090] The solar cell of the present invention will now be
explained.
[0091] In the solar cell of the present invention, optimization of
the design and the circuit design against sunlight are carried out,
as an embodiment of a photoelectric conversion element of the
present invention, to provide a structure by which optimum
photoelectric conversion is obtained when sunlight is utilized as a
light source. That is, a structure in which a dye sensitized oxide
semiconductor is capable of being irradiated with sunlight. At the
time of fabricating a solar cell of the present invention, it is
preferable that the aforesaid oxide semiconductor, charge transfer
layer and counter electrode are stored in a sealed case or the
whole members are sealed with resin.
[0092] When the solar cell of the present invention is irradiated
with sunlight or electromagnetic waves equivalent to sunlight, the
dye adsorbed on an oxide semiconductor absorbs irradiated sunlight
or electromagnetic waves to be excited. An electron generated by
the excitation is transferred to the semiconductor and successively
to the conductive support. Then the electron is transferred through
an external circuit to the counter electrode where the electron
reduces the redox electrolyte in the charge transfer layer. On the
other hand, the dye of the present invention, which has given the
electron to the semiconductor, is in an oxidized state, however,
returns to the original reduced state by receiving an electron from
the counter electrode via the redox electrolyte in a charge
transfer layer. Simultaneously, the redox electrolyte in a charge
transfer layer returns again to an oxidized state capable of being
reduced with an electron supplied from the counter electrode. The
electrons flows in this manner, and the solar cell utilizing the
photoelectric conversion element of the present invention can be
thus constituted.
EXAMPLES
[0093] In the following, the present invention will be explained
referring to examples, however the present invention is not limited
thereto.
Example 1
Preparation of Photoelectric Conversion Element 1
[0094] Titanium oxide paste (a particle diameter of 18 nm)
available on the market was applied on a glass substrate provided
with a fluorine-doped tin oxide (FTO) conductive layer (a FTO
coated glass substrate) by a doctor blade method. The paste, after
having been dried by heating at 60.degree. C. for 10 minutes, was
subjected to a calcination treatment at 500.degree. C. for 30
minutes, whereby a titanium oxide thin film having a thickness of 5
.mu.m was prepared.
[0095] Dye (1) was dissolved in ethanol to prepare a solution of
3.times.10.sup.-4 M (mole/liter). The FTO coated glass substrate on
which titanium oxide had been applied and calcinated was immersed
in the above solution for 16 hours at room temperature to perform
an adsorption treatment of the dye, whereby an oxide semiconductor
electrode was prepared.
[0096] As a charge transfer layer (a liquid electrolyte), a
3-methylpropionyltrile solution containing 0.4 M of lithium iodide,
0.05 M of iodine and 0.5 M of 4-(t-butyl)pyridine was utilized. A
platinum plate was utilized as a counter electrode, and
photoelectric conversion element 1 was prepared by assembling
together with an oxide semiconductor electrode and a liquid
electrolyte, which had been prepared in advance, by use of a cramp
cell.
Preparation of Photoelectric Conversion Elements 2-10
[0097] Photoelectric conversion elements 2-10 were prepared in a
similar manner to preparation of Photoelectric conversion element 1
except that dyes (2)-(8), a comparative dye and a Ru complex
(dithiocyanato-bis(2,2'-pyridyl-4,4'-dicarboxylato)ruthenium) each
were utilized as shown in Tables 1 and 2 instead of dye (1).
##STR00012##
[0098] [Evaluation]
[0099] Under irradiation of a xenon lamp at an intensity of 100
mW/cm.sup.2, photoelectric conversion characteristics were measured
under a condition of covering an oxide semiconductor electrode with
a mask of 5.times.5 mm.sup.2.
[0100] That is, with respect to photoelectric conversion elements
1-10, a current-voltage characteristic at room temperature was
measured by use of an I-V tester, whereby a short circuit current
(Jsc), an open circuit voltage (Voc) and a filling factor (F. F.)
were determined, and photoelectric conversion efficiency (.eta.(%))
was determined from them. The photoelectric conversion efficiency
(.eta.(%)) of a photoelectric conversion element was calculated
based on following Equation (A).
.eta.=100.times.(Voc.times.Jsc.times.F.F.)/P Equation (A)
wherein, P is an incident light intensity [mW/cm.sup.2], Voc is an
open circuit voltage [V], Jsc is a short circuit current density
[mA/cm.sup.2] and F. F. is a filling factor.
[0101] Further, after an oxide semiconductor electrode had been
exposed to an ozone atmosphere of 9 ppm for 20 minutes, variation
of the photoelectric conversion characteristics was observed.
[0102] Table 1 shows the results of the characteristics evaluation
of the photoelectric conversion elements before ozone exposure, and
Table 2 shows the results of the characteristics evaluation of the
photoelectric conversion elements after ozone exposure. Further, in
Table 2, ratios of the photoelectric efficiencies before and after
ozone exposure are shown. The ratio of the photoelectric conversion
efficiencies before and after ozone exposure is given by the
following equation:
(Ratio of conversion efficiency before and after ozone
exposure)=(Photoelectric conversion efficiency after ozone
exposure)/(Photoelectric conversion efficiency before ozone
exposure)
wherein "Ratio of conversion efficiency" represent the ratio of the
photoelectric conversion efficiencies.
TABLE-US-00001 TABLE 1 Short Photoelectric Open circuit circuit
Conversion conversion voltage current Filling efficiency element
Dye (V) (mA cm.sup.-2) factor (%) Remarks 1 (1) 0.76 5.6 0.54 2.3
Invention 2 (2) 0.64 2.0 0.60 0.8 Invention 3 (3) 0.74 5.6 0.56 2.4
Invention 4 (4) 0.71 5.9 0.58 2.4 Invention 5 (5) 0.73 4.7 0.55 1.9
Invention 6 (6) 0.68 3.8 0.61 1.6 Invention 7 (7) 0.68 6.3 0.54 2.3
Invention 8 (8) 0.70 4.4 0.56 1.7 Invention 9 Comparative 0.68 3.9
0.52 1.4 Comparison dye 10 Ru complex 0.77 6.0 0.52 2.4
Comparison
TABLE-US-00002 TABLE 2 Ratio of conversion Open Short efficiency
Photoelectric circuit circuit Conversion before and conversion
voltage current Filling efficiency after ozone element Dye (V) (mA
cm.sup.-2) factor (%) exposure Remarks 1 (1) 0.59 2.8 0.57 0.95
0.41 Invention 2 (2) 0.47 1.1 0.59 0.31 0.40 Invention 3 (3) 0.59
2.3 0.58 0.80 0.34 Invention 4 (4) 0.61 3.0 0.56 1.02 0.43
Invention 5 (5) 0.57 2.1 0.60 0.72 0.38 Invention 6 (6) 0.55 1.9
0.57 0.59 0.37 Invention 7 (7) 0.60 2.2 0.61 0.81 0.35 Invention 8
(8) 0.58 2.0 0.59 0.68 0.40 Invention 9 Comparative 0.51 1.4 0.61
0.42 0.31 Comparison dye 10 Ru complex 0.28 0.22 0.42 0.03 0.01
Comparison
[0103] From the ratios of the photoelectric conversion efficiencies
between and after the ozone exposure shown in Tables 1 and 2, it is
clear that any of triphenyamine dyes (1)-(8) and comparative dye
has anti-oxidation durability significantly superior than that of
the Ru complex. In particular, it is clear that dyes (1)-(8) of the
present invention, which have a styryl structure, exhibited higher
anti-oxidation durability compared to the comparative dye without a
styryl structure, and that introduction of a styryl structure into
triphenylamine central moiety is effective as a guide to obtain a
sensitizing dye having a high durability.
* * * * *